switch to expand and adapt test case accordingly

as discussed with @jglick as the intention of the flatten plugin here is to have
a self contained pom - this will switch to expand which will also have the benefit
of picking up any <dependencyManagement> configured in the parent(s).

pom.xml

@@ -27,7 +27,7 @@
 
   <groupId>org.jenkins-ci.plugins</groupId>
   <artifactId>plugin</artifactId>
-  <version>4.56-SNAPSHOT</version>
+  <version>4.56-flatten-expand-SNAPSHOT</version>
   <packaging>pom</packaging>
 
   <name>Jenkins Plugin Parent POM</name>
@@ -1313,9 +1313,9 @@
                 </goals>
                 <phase>process-resources</phase>
                 <configuration>
-                  <!-- flattenMode:oss does not keep dependecnyMangement or will promote all transitive dependencies to direct ones, changing resolution order -->
+                  <!-- flattenMode:oss does not keep dependencyMangement or will promote all transitive dependencies to direct ones, changing resolution order -->
                   <pomElements>
-                    <dependencyManagement>interpolate</dependencyManagement>
+                    <dependencyManagement>expand</dependencyManagement>
                     <!-- from https://github.com/mojohaus/flatten-maven-plugin/blob/flatten-maven-plugin-1.3.0/src/main/java/org/codehaus/mojo/flatten/FlattenMode.java#L100 -->
                     <ciManagement>expand</ciManagement>
                     <contributors>expand</contributors>

src/it/incrementals-and-plugin-bom/postbuild.groovy

@@ -4,16 +4,10 @@ String pomXml = new File(basedir, '../../local-repo/io/jenkins/plugins/increment
 assert pomXml.contains('version>1.0-rc1234.deadbeef5678</version>')
 // https://github.com/jenkinsci/plugin-pom/issues/705
 // line endings need normalising
-assert pomXml.replace("\r\n", "\n").contains('''
-  <dependencyManagement>
-    <dependencies>
-      <dependency>
-        <groupId>io.jenkins.tools.bom</groupId>
-        <artifactId>bom-2.361.x</artifactId>
-        <version>1580.v47b_429a_c853a</version>
-        <type>pom</type>
-        <scope>import</scope>
-      </dependency>
-    </dependencies>
-  </dependencyManagement>'''.replace("\r\n", "\n"))
+assert pomXml.matches('(?s).*<dependencyManagement>\\s*<dependencies>'
+// something from the parent pom dependencyManagement
++ '.*<dependency>\\s*<groupId>javax.servlet</groupId>\\s*<artifactId>javax.servlet-api</artifactId>\\s*<version>3.1.0</version>\\s*</dependency>'
+// something from the bom
++ '.*<dependency>\\s*<groupId>io.jenkins.plugins</groupId>\\s*<artifactId>caffeine-api</artifactId>\\s*<version>2.9.3-65.v6a_47d0f4d1fe</version>\\s*</dependency>'
++ '.*</dependencies>\\s*</dependencyManagement>.*')
 return true